Ab initiophase diagram of oxygen adsorption on W(110)

Abstract

The phase diagram of oxygen adsorption on the W(110) surface is derived without any empirical parameters by a combination of density functional theory (DFT) calculations, the cluster expansion (CE) technique and Monte Carlo (MC) applications. Coverages up to 1 monolayer are considered corresponding to the range of oxygen concentrations, 0≤x(O)≤1. DFT results for single-site adsorption and in particular for full coverage reveal that adsorption at threefold hollow (H3) sites is by far the most stable one. Therefore, the CE is done for an atomic layer with the two H3 sublattices of the W(110) surface. Based on 60 DFT calculations with fully relaxed atomic geometries of lateral unit cells containing 12 atoms, and a ground state search for 80 394 structures, four ground state structures are found with the lateral unit cells (2 × 5) for x(O) = 0.20, (2 × 2) (a) for x(O) = 0.25, (2 × 1) for x(O) = 0.50 and (2 × 2) (b) for x(O) = 0.75. In agreement with experiments the most stable structures are (2 × 1) and (2 × 2) (b), which correspond to higher coverages. The thermodynamical stability of the two ground states at lower coverages is very weak. Detailed analysis of the relaxation of the (2 × 1) structure reveals sizeable lateral stresses acting on the surface tungsten atoms. On the basis of the effective cluster interactions MC simulations are performed in order to derive the critical temperatures by which the phase diagram is finally constructed.

First-principles Thermodynamic Models in Heterogeneous Catalysis

“…In this chapter we describe an approach that requires no prior knowledge of the underlying interaction mechanisms. The DFT results for a number of adsorbate configurations are used to parameterize a cluster expansion (CE) model, [18][19][20][21][22][23][24][25][26][27] a type of Ising Hamiltonian, that reduces the adsorption energy to a function of adsorption site occupancies and site-site interactions. Such CE models can give significant insight into the dominant interactions controlling the behavior of the system.…”

Oxidation of W(110) studied by LEED and STM

“…This position is known to be the most energetically favorable position for oxygen on the W(110) and Mo(110) surface. As one moves from this point to the right, along the W[11 1] direction the oxygen atoms are located on a two fold site, and then their position moves gradually towards the least energetically favorable (1.2 eV higher), on-top position [29]. However, after 8 units, we see that there is a shift and the 9th oxygen atom is located again on the 3-fold site.…”

Adsorption and Reactions of Carbon Monoxide and Oxygen on Bare and Au-Decorated Carburized W(110)

“…The modifications of the Au clusters induced by exposure to O 2 as seen by STM could then be explained by a displacement of Au atoms due to the competitive adsorption of dissociated oxygen for (the same) favorable adsorption sites. Because of the large binding energy of oxygen to tungsten (adsorption energy 4.20 eV/atom 62 ), we expect that the carbon-poor regions where the Au clusters nucleate are also the most favorable areas for oxygen adsorption, thus providing a strong driving force for an oxygen-induced rearrangement of the noble-metal clusters. However, as the oxygen atoms on W(110) are bound rather strongly to the surface, we expect that they are not available for the low-temperature formation of CO 2 , leading to the conclusion that also for this reason the system—despite its ability to dissociate molecular oxygen—will not be able to perform CO combustion.…”